I've never worked for Debenhams, but I have had phone interviews. The main questions they seem to ask are about experiences, just the usual:
Can u give me an example of a time when you worked as part of a team to overcome a problem? What was the problem? How did you resolve it? What was your role in that team?
Can you give an example of when you went above and beyond what was expected?
Can you give an example of when you didn't get on well with a member of a team? What did you do? What was the outcome?
As long as you have a few example of work or personal experiences you can relate to you'll be fine. Write them down and have them in front of you. Best of luck! x